Embodiments described herein relate generally to switch fabrics and more particularly to flow-control of switch fabrics such as Clos networks.
Clos networks are multi-stage switch networks that provide non-blocking connections between multiple input ports and multiple output ports. A non-blocking network is a network in which a data path through the network can always be established between an idle input port and an idle output port.
A three-stage Clos network, for example, has a middle stage connected between an input stage and an output stage. Each stage includes a plurality of modules. Each input stage module has multiple input ports (n) and is operatively coupled to each middle stage module. Similarly, each output stage module has n output ports and is connected to each middle stage module.
A circuit switched switch fabric is a switch fabric in which a dedicated data path is established between an input port and an output port before data is sent through the switch fabric. Thus, once the dedicated data path is established, the data is sent from the input module to the output module over the dedicated data path. In contrast, a cell switched switch fabric is a switch fabric that reroutes data packets at each stage of the switch fabric. Accordingly, no dedicated path is needed to send the data packets from an input port to an output port.
In a cell switched Clos network, if multiple data packets are sent to a single module within a stage of the switch fabric, transient congestion can occur. One solution to such a problem is to buffer the data within the modules prior to sending data to the next stage. Having a large buffering capacity on each module, however, is expensive and undesirable. Additionally, if the modules have a small buffering capacity, the modules might be forced to drop data due to lack of capacity. Dropping data due to transient congestion is also undesirable.
Thus, a need exists for a flow-control solution in a switch fabric that limits transient congestion and loss of data. Further, a need exists for a low-cost, effective, flow-control solution.